Polyamide resins have excellent thermal deformation resistance, rigidity and oil resistance and are used in electric appliance parts and automobile parts. Further improvement in impact strength and water resistance is desired, however.
As regards the impact strength, in particular, various attempts have already been made, including, more specifically, the use of ABS resins and modified polyolefins.
On the other hand, impact modifiers of the core-shell polymer type have been proposed, with a rubbery polymer as the core and a glassy polymer as the shell. Impact modifiers of this kind show good dispersibility in resins and it is relatively easy to attain reproducibility from the morphology viewpoint.
A core-shell polymer for improving the impact strength of polyamide resins has already been proposed in U.S. Pat. No. 3,668,274 AND EP-51,471, each of which polymer contains carboxyl groups in the shell phase. Compositions composed of this carboxyl-modified core-shell polymer and nylon 6 indeed show good notched Izod impact strength (thickness: 1/8 inch) at temperatures not lower than 23.degree. C. but still have problems: the impact strength is low and the melt viscosity is high. The latter fact offers a problem from the moldability viewpoint.
In the pigment-related technical field, core-shell polymers whose core and shell phases are both modified with a carboxylic acid(s) are known (Japanese Kokai Tokkyo Koho Nos. 63-213509 and 61-185505). However, they cannot be used as impact modifiers for polyamide resins.